Here's why:
* Tonight refers to the current night. It's a specific point in time.
* Present form is used for verbs, which describe actions or states of being.
Examples:
* Incorrect: "Tonight is going to be a great night." (Tonight is not a verb.)
* Correct: "I'm going to the movies tonight." (The verb "going" is in the present form.)
To use "tonight" correctly, you need to combine it with a verb in the present tense.